This invention relates to an oscillator circuit comprising:
an amplifier which can be controlled by means of a control voltage on a control terminal and which comprises a feedback circuit which is arranged between an amplifier input and an amplifier output;
an amplitude controller which comprises an amplitude detector for controlling the oscillation amplitude in dependence on a detected amplitude and also comprises a first and a second current source for supplying currents of mutually opposed polarity to the control terminal, at least one of the current sources being controllable by the amplitude controller.
An oscillator circuit of this kind is known from FIG. 2 of European Patent Application EP No. 50.583, or equivalent U.S. Pat. No. 4,433,371. As is known, a voltage control system comprising two current sources supplying currents of different polarity to the control terminals constitutes a sensitive control system because of the high impedance of a current source. Small current variations are then converted into large voltage variations.
In the known oscillator circuit there is generated a control voltage which is dependent on negative as well as of positive fluctuations of the oscillation voltage. For stable control it is then necessary to stabilize the mean value of the control voltage, necessitating additional steps in the form of additional components. Additional components, however, imply additional noise sources and additional substrate surface area in an integrated circuit. Therefore, the invention inter alia aims to provide an oscillator circuit of the kind set forth which has a simpler set-up and which comprises fewer components.